It is well known that in order to optimize and maximize the performance and life of an electric vehicle battery, the charge levels of the constituent components or elements of the battery, such as, for example, the individual cells or groups of cells of a battery pack, must be periodically balanced or equalized. Such balancing operations, which may be referred to below as “cell balancing” or “cell balancing operations,” may be performed using any number of known methodologies or techniques.
One such technique is a passive/resistive cell balancing technique where, in one implementation, each cell (or groups of cells) of a battery pack is electrically connected to a respective balancing/sensing circuit that is configured to provide a means for both balancing the corresponding cell and sensing or measuring electrical parameters relating thereto (e.g., cell voltage). More particularly, in one particular implementation, each balancing/sensing circuit comprises a series combination of a balancing switch and a balancing resistive element (e.g., resistor) that is electrically connected in parallel with the corresponding cell by a pair of sense wires. Additionally, for purposes of diagnosing whether the balancing switch is operational, one or both of the sense wires of the balancing/sensing circuit may include a resistive element (e.g., resistor) that is electrically connected in series to both the cell and the series combination of the balancing switch and balancing resistive element. The inclusion of one or more series resistive elements in the sense wire(s) serves to form a voltage divider within the balancing/sensing circuit (i.e., the series combination of the series resistive element and the balancing resistive element form a voltage divider) and, as a result, causes a voltage drop when the balancing switch is in a “closed” or “on” state and current flows from the cell through the balancing resistive element. When a battery control module, or some other suitable vehicle component, senses or detects such a voltage drop, it may determine that the balancing switch is, in fact, operational, otherwise it may determine that there may be a problem with the balancing switch.
This particular cell balancing technique is not without its drawbacks, however. For example, because of the voltage divider formed in the balancing/sensing circuit, when a balancing switch corresponding to a particular cell is in the “closed” or “on” state during, for example, a cell balancing operation, the voltage measured across the series combination of the balancing switch and balancing resistive element is lower than the actual voltage of the cell. Accordingly, any voltage measurements taken or made while the balancing switch is closed, and therefore, any voltage measurements taken or made during the performance of a cell balancing operation, are effectively useless for any purpose requiring accurate cell voltage measurements (e.g., for the purpose of controlling the cell balancing operation), and thus, must be discarded. As such, the availability of useful cell voltage information and the speed at which such information can be obtained, as well as the sophistication and speed of controls that use such information, is adversely impacted by the lowered or reduced voltage measurements.